Radiation sensitive marking and process utilizing same

ABSTRACT

A bicyclo-heptene-7-one serves as a radiation indicator. Upon exposure to a sufficient dose of electrons the indicator exhibits fluorescence in ultraviolet light.

United States Patent [1 1 Chandross et al.

[ 1 Aug. 12, 1975 RADIATION SENSITIVE MARKING AND PROCESS UTILIZING SAME [75] Inventors: Edwin Arthur Chandross, Murray Hill; Coralie Anne Pryde, Morristown; Warren Allen Salmon, Summit, all of NJ.

[7 3] Assignee: Bell Telephone Laboratories,

Incorporated, Murray Hill, NJ.

22 Filed: Mar. 20,1974

[21] Appl. No.: 452,850

[52] US. Cl 250/484; 250/461 [51] Int. Cl. G01N 21/38 [58] Field of Search 250/461, 484

[56] References Cited UNITED STATES PATENTS 3,639,762 2/1972 Hughes 250/461 X 3,801,782 4/1974 Dorion 250/461 X 3,808,443 4/1974 Chandross et al. 250/484 Primary ExaminerArchie R. Borchelt Attorney, Agent, or Firm-G. S. Indig [5 ABSTRACT A bicyclo-heptene-7-one serves as a radiation indicator. Upon exposure to a sufficient dose of electrons the indicator exhibits fluorescence in ultraviolet light.

13 Claims, 2 Drawing Figures RADIATION SENSITIVE MARKING AND PROCESS UTILIZING SAME BACKGROUND OF THE INVENTION 1. Field Of The Invention The invention is concerned with means for detennining the irradiation history of objects exposed to electron radiation.

2. Description Of The Prior Art Electron beam irradiation is used on an industrial scale for a variety of purposes, a prominent application being the crosslinking of polymers such as polyvinylchloride (PVC). For instance, in the manufacture of insulated wire, electron beam irradiation is applied to the PVC coated wire in order to toughen the insulating coating and to increase its resistance to heat and abrasion. Electron beam irradiation is also used in the manufacture of heat-shrinkable film and plastic rivets and for the sterilization of medical supplies.

Since, typically, there is no change of appearance due 'to the irradiation of an object, there is a need for a process control for determining whether or not a supposedlyirradiated object has indeed been exposed to the intended radiation dose. Of particular interest are indicators integral to the surface of the irradiated object. Among these are the so-called dye dosimeters which change color or color intensity upon exposure to radiation; several such dosimeters are described in A. Charlesby, Atomic Radiation and PoIymers, pergamon Press, I960, Chapter 6. However, the use of a dye may be undesirable for a variety of reasons. For instance, its use may be detrimental to the appearance of an object, or the color of the object may be too intense to serve as a background for a dye. To deal with such cases an alternate method was proposed in W. A. Salmon and E. A. Chandross, A Fluorescent Integrating Radiation Dosimeter," Analytical C/zemisty 45, 2446 I973 This indicator uses the photodimer of amyl anthroate, a colorless substance which is broken to the monomer by electron beam irradiation. The monomer fluoresces brightly when exposed to ultraviolet light, whereas the dimer does not. This indicator is easily made an integral part of the object to be irradiated by applying it in solution as a marking. Furthermore, its application leaves the appearance of the object unchanged, as desired. However, the costs of the anthroic ester and of the process of photodimerization are such that the marking, when applied to PVC-insulated wire, significantly adds to the cost of the product.

SUMMARY OF THE INVENTION The invention is based on a chemical reaction which occurs when a poly-arylated bicyclo-[2,2,l]-heptene- 7-one is irradiated with electrons. Such a substance either is fluorescent or invisible in ultraviolet light, depending on whether or not it has been exposed to a sufficient dose of radiation, respectively.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows PVC-insulated wire marked, as taught by the invention, with a radiation indicator being exposed to electron beam; and

FIG. 2 shows PVC-insulated wire marked, as taught by the invention, with a radiation indicator being exposed to ultraviolet light.

Detailed Description I. The Drawing FIG. 1 shows electrical wire 11 coated with PVC insulation 12, marked with electron sensitive indicator I3, and being irradiated with electron beam 14 emanating from electron source 15.

FIG. 2 shows electrical wire 21 coated with PVC insulation 22, marked with indicator 23 being irradiated with ultraviolet light 24 emanating from source 25 equipped with filter 28. Visible light 26 emanating from indicator 23 is sensed by light detector 27.

2. Chemical Manufacture of the Indicator The bicyclo-heptene-7-one, the active ingredient of the indicator, may be obtained by so-called Diels-Alder addition of a poly-arylated cyclopentadienone and a dienophile. Among dienophiles suitable for the purpose of the invention are styrene, maleic anhydride, and acenaphthylene. Typically, the synthesis of the adduct is carried out by heating, in benzene solution, an excess of the dienophile with the cyclopentadienone.

The following diagram specifically shows the Diels- Alder reaction of tetra-arylated cyclopentadienone with styrene:

l l H X C H t T l o l /c=0+ ll I A c z H/ n \l/T\ X| ,IQ H

In the diagram, the symbols X X X and X denote aryl groups which may contain alkyl or alkoxy substituents. These aryl groups may be different; manufacturing of the indicator is facilitated, however, if X, is the same as X and if X, is the same as X,

Dienophiles used in the manufacture of the marking may be carbocyclic or heterocyclic. However, in order to avoid undesirable decarbonylation in ultraviolet light, such dienophiles should not contain more than three rings.

A comprehensive account of the preparation and chemical properties of Diels-Alder adducts is given in A. J. Onishchenko, Diene Synthesis, D. Davey, New York 1964, Chapters 3 and 5.

3. Fluorescence of the Indicator The aryla'ted bicycle-[2,2,1]-heptene-7-ones are not fluorescent when exposed to soft ultraviolet light, i.e., to electromagnetic radiation of wavelength greater than 300 nanometers and less than 400 nanometers.

Upon irradiation with a sufficient dose of electrons adducts lose the carbonyl bridge as specifically shown in the following diagram for the cyclopentadienoneand-styrene adduct:

The resulting cyclohexa-l,3-diene, when exposed to soft ultraviolet light, does exhibit fluorescence. To be r I useful as a positive indicatorfor electron radiation, the r marking should be protected from hard ultraviolet light, i.e., from electromagnetic radiation of wavelength less than 300 nanometers. This is because such light, like electrons, causes decarbonylation and thus fluorescence in soft ultraviolet light. When a source is used which emits soft as well as hard ultraviolet radia tion, such protection is easily provided, for instance, by means of a filter blocking the undesirable hard radiation. Also, for the sake of positive indication the light source should not emit significant amounts of visible light. Specifically, the reading light should be restricted to wavelengths less than 400 nanometers. Finally, since decarbonylation occurs also at elevated temperatures, the marking must not be exposed to heat. Since no appreciable thermal decarbonylation occurs at temperatures up to 150C, the indicator is stable at normal storage temperature.

When dissolved in a'liquid which, upon drying, acts as a binder, the marking can be applied directly to the surface of an object by painting or spraying in any desired pattern. Solvents suitable for this purpose are polymer carriers such as polystyrene which not 'only acts as a solvent but also enhances the sensitivity of the marking; Hence, when dissolved in polystyrene rather than in a nonenhancing binder, a lesser amount of the ingredient is sufficient to achieve a desired sensitivity. For example, a -10 micrometer thick marking of percent tetracyclone-and-acenaphthylene adduct in polystyrene is suitable as a dosimeter for a radiation forms by decarbonylation into a cyclohexal,3-diene,

whereby the said indicator is rendered fluorescent when exposed to ultraviolet light including a wavelength within the range of from 300 to 400 nanometers. 2. Article of claim 1, in which said body of material comprises a polymer and an electron-sensitive crosslinking agent.

3. Article of claim 2 in which said polymer electrically insulates an electrical conductor.

4. Article of claim 2 in which said polymer comprises polyvinylchloride insulation of an electrical conductor.

5. Article of claim 1 in which said compound is a 1,4-

adduct of an alkene and poly-arylated tetracyclone.

6. Article of claim 5 in which said alkene contains up to three rings.-

7. Article of claim 6 in which said alkene is selected from the .group consisting of styrene, maleic anhydride,

' and acenaphthylene.

are such that the aryl group in position 1 is chemically dose of 5 Mrads as it is employed in crosslinking PVC wire insulation.

While application of the marking directly to the surface to be irradiated is the preferred embodiment of the invention, use of an auxiliary member carrying the indicator is not precluded. For example, the marking may be applied in the form of a tape impregnated with the bicyclo-heptene-7-one and made to adhere to an object prior to irradiation.

What is claimed is:

1. Article of manufacture comprising a body of a material whose processing comprises exposure to electron radiation characterized in that at least a portion of said articles surface includes a radiation indicator comprising, prior to electron irradiation, a compound which is a polyarylated bicycle-[2,2,1 ]-heptene-7-one which, when irradiated with electrons, at least in part transthe same as the aryl group in position 4 and the aryl group in position 2 is chemically the same as the aryl group in position 3.

10. Article of Claim 1 in which said indicator is a surface layer of a thickness of from l-lOO micrometers.

11. Article of claim 10 in which said indicator includes a binder medium enhancing adhesion to said article.

12. Article of claim 11 in which said binder medium comprises polystyrene.

13. Process for fabricating an article in accordance with a schedule which comprises exposing said article to electron radiation, characterized by providing said article with a radiation detector material, said material comprising a compound which is a poly-arylated bicylco-[ 2,2,1 ]-heptene-7-one which, when irradiated with electrons, at least in part transforms by decarbonylation into a cyclohexa-l,3-diene,

exposing said electron irradiated article to ultraviolet light including, a wavelength within the range of from 300 to 400nanometers, and v detecting fluorescence emanating from said radiation detector material whereby exposure to electrons is confirmed by the presence of fluorescence. 

1. ARTICLE OF MANUFACTURE COMPRISING A BODY OF A MATERIAL WHOSE PROCESSING COMPRISES EXPOSURE TO ELECTRON RADIATION CHARACTERIZED IN THAT AT LEAST A PORTION OF SAID ARTICLE''S SURFACE INCLUDES A RADIATION INDICATOR COMPRISING, PRIOR TO ELECTRON IRRADIATION, A COMPOUND WHICH IS A POLYARYLATED BICYCLO(2,2,1)-HEPTENE-7-ONE WHICH, WHEN IRRADIATED WITH ELECTRONS, AT LEAST IN PART TRANSFORMS BY DECARBONYLATION INTO A CYCLOHEXA-1,3-DIENE, WHEREBY THE SAID INDICATOR IS RENDERED FLUORESCENT WHEN EXPOSED TO ULTRAVIOLET LIGHT INCLUDING A WAVELENGTH WITHIN THE RANGE OF FROM 300 TO 400 NANOMETERS.
 2. Article of claim 1, in which said body of material comprises a polymer and an electron-sensitive crosslinking agent.
 3. Article of claim 2 in which said polymer electrically insulates an electrical conductor.
 4. Article of claim 2 in which said polymer comprises polyvinylchloride insulation of an electrical conductor.
 5. Article of claim 1 in which said compound is a 1,4-adduct of an alkene and poly-arylated tetracyclone.
 6. Article of claim 5 in which said alkene contains up to three rings.
 7. Article of claim 6 in which said alkene is selected from the group consisting of styrene, maleic anhydride, and acenaphthylene.
 8. Article of claim 5 in which at least one of the four aryl groups in said poly-arylated tetracyclone has alkyl or alkoxy substituents.
 9. Article of claim 8 in which said four aryl groups are such that the aryl group in position 1 is chemically the same as the aryl group in position 4 and the aryl group in position 2 is chemically the same as the aryl group in position
 3. 10. Article of Claim 1 in which said indicator is a surface layer of a thickness of from 1-100 micrometers.
 11. Article of claim 10 in which said indicator includes a binder medium enhancing adhesion to said article.
 12. Article of claim 11 in which said binder medium comprises polystyrene.
 13. Process for fabricating an article in accordance with a schedule which comprises exposing said article to electron radiation, characterized by providing said article with a radiation detector material, said material comprising a compound which is a poly-arylated bicylco-(2,2,1)-heptene-7-one which, when irradiated with electrons, at least in part transforms by decarbonylation into a cyclohexa-1,3-diene, expOsing said electron irradiated article to ultraviolet light including a wavelength within the range of from 300 to 400 nanometers, and detecting fluorescence emanating from said radiation detector material whereby exposure to electrons is confirmed by the presence of fluorescence. 